• Human 5-HT7(a) receptor;
  • long splice variant;
  • functional characterisation;
  • adenylyl cyclase;
  • [3H]-5-CT binding;
  • constitutive receptor activity;
  • inverse agonism;
  • SB-258719
  • 1
    The functional profile of the long form of the human cloned 5-HT7 receptor (designated h5-HT7(a)) was investigated using a number of 5-HT receptor agonists and antagonists and compared with its binding profile. Receptor function was measured using adenylyl cyclase activity in washed membranes from HEK293 cells stably expressing the recombinant h5-HT7(a) receptor.
  • 2
    The receptor binding profile, determined by competition with [3H]-5-CT, was consistent with that previously reported for the h5-HT7(a) receptor. The selective 5-HT7 receptor antagonist SB-258719 ((R)-3,N-Dimethyl-N-[1-methyl-3-(4-methylpiperidin-1-yl)propyl]benzene sulfonamide) displayed high affinity (pKi 7.5) for the receptor.
  • 3
    In the adenylyl cyclase functional assay, 5-CT and 8-OH-DPAT were both full agonists compared to 5-HT and the rank order of potency for agonists (5-CT>5-HT>8-OH-DPAT) was the same in functional and binding studies.
  • 4
    Risperidone, methiothepin, mesulergine, clozapine, olanzapine, ketanserin and SB-258719 antagonised surmountably 5-CT-stimulated adenylyl cyclase activity. Schild analysis of the antagonism by SB-258719 gave a pA2 of 7.2±0.2 and slope not significantly different from 1, consistent with competitive antagonism.
  • 5
    The same antagonists also inhibited basal adenylyl cyclase activity with a rank order of potency in agreement with those for antagonist potency and binding affinity. Both SB-258719 and mesulergine displayed apparent partial inverse agonist profiles compared to the other antagonists tested. These inhibitory effects of antagonists appear to be 5-HT7 receptor-mediated and to reflect inverse agonism.
  • 6
    It is concluded that in this expression system, the h5-HT7(a) receptor shows the expected binding and functional profile and displays constitutive activity, revealing inverse agonist activity for a range of antagonists.

British Journal of Pharmacology (1998) 124, 1300–1306; doi:10.1038/sj.bjp.0701946